Alignment weight for floating field pin design

ABSTRACT

An alignment weight is provided. The alignment weight includes a body of material having first and second opposing surfaces. A number of depressions are formed in the first surface. The depressions receive pins of a floating pin field when placed on a floating pin field during connection of the floating pin field to a printed circuit board.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of electroniccircuits and, in particular, to an alignment weight for an electroniccircuit with a floating pin field design.

BACKGROUND

Integrated circuits are a common part of modern electronic equipment.Integrated circuits typically include a large number of transistors andother circuit elements that are interconnected on a common semiconductorchip or die. Typically, integrated circuits are packaged independentlyand interconnected on a printed circuit board for installation in anelectronic system, such as a computer.

A printed circuit board can be connected to an electronic system in anumber of ways. For example, a printed circuit board can include a“floating pin field” on one side of the printed circuit board. Thefloating pin field includes a number of pins that are held in a fixedspatial relation by a pin field carrier through which the pins pass. Thepins are electrically connected to circuit elements on the printedcircuit board. A floating pin field design may be used, for example,with a printed circuit board containing an upgraded processor for acomputer.

When a floating pin field design is used, the printed circuit board maybe connected to a system through a socket such as a socket located on amother board of a computer system. The socket typically includes anumber of receptacles that are placed around a perimeter of the socket.The receptacles receive the pins of the floating pin field.

One problem with printed circuit boards that use a floating pin fielddesign is in the process for soldering the pins to the bottom of theprinted circuit board. Generally, the pins are held in place with a pinfield carrier. The printed circuit board is patterned with a solderpaste at the locations where the pins are to connect to the printedcircuit board. The pins and the pin field carrier are placed on theboard and the solder undergoes a reflow process. Unfortunately,sometimes not all of the solder joints created with this reflow processprovide acceptable connection between the pin and the circuit elementson the printed circuit board. For example, so-called “solderbridges”—solder material that extends over a significant distancebetween a pin and the printed circuit board—can be formed, for example,when a pin moves away from the printed circuit board during the reflowprocess. These solder bridges provide a poor, brittle mechanicalconnection for the pin and can lead to open solder joints during use.Furthermore, when an open solder joint is detected after production, thepart is typically disposed of since rework of the open solder joints isoverly burdensome. This can result in a significant waste of resourcesin fabricating electronic modules using floating pin fields.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art fora more reliable technique for producing acceptable solder joints in anelectronic module using a floating pin field design.

SUMMARY

The above mentioned problems with electronic modules using a floatingpin field design and other problems are addressed by the presentinvention and will be understood by reading and studying the followingspecification. An alignment weight is described which is used to holdthe pins in place during a reflow process.

In one embodiment, an alignment weight is provided. The alignment weightincludes a body of material having first and second opposing surfaces. Anumber of depressions are formed in the first surface. The depressionsreceive pins of a floating pin field when placed on a floating pin fieldduring connection of the floating pin field to a printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative embodiment of analignment weight according to the teachings of the present invention.

FIG. 2 is a bottom view of the alignment weight of FIG. 1.

FIG. 3 is a cross-sectional view of a portion of an embodiment of anelectronic module during production with an alignment weight in placeaccording to the teachings of the present invention.

FIG. 4 is a perspective view of an embodiment of an electronic systemmodule with a floating pin field constructed using the alignment weightaccording to the teachings of the present invention.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingswhich form a part of the specification. The drawings show, and thedetailed description describes, by way of illustration specificillustrative embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be used andlogical, mechanical and electrical changes may be made without departingfrom the scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense.

FIG. 1 is a perspective view of an illustrative embodiment of analignment weight indicated generally at 100 and constructed according tothe teachings of the present invention. Alignment weight 100 is used ina process for connecting pins of a floating pin field to a printedcircuit board. Specifically, alignment weight 100 is designed to providea downward force that helps to secure pins in place during a solderreflow process and to maintain the pins in a substantially straight-upalignment. Advantageously, alignment weight 100 also maintains the endsof the pins of the floating pin field substantially in the same plane.

Alignment weight 100 is formed from a material that can withstand theheat of a solder reflow process without significant warping. Further,the material has sufficient weight to provide downward force on the pinsto assure the creation of an acceptable solder joint. For example, inone embodiment, alignment weight 100 is formed from Ultem®PolyEtherimide material, e.g., Ultem® 2300, commercially available fromEnsiger Corporation. Ultem is an amber transparent high performancepolymer which combines high strength and rigidity at elevatedtemperatures with long term heat resistance. Other appropriate materialscan be used to produce the body of alignment weight 100.

Alignment weight 100 includes first and second opposing surfaces 104 and106, respectively. Surface 106 includes a number of depressions 108.Depressions 108 are disposed in surface 106 in positions that correspondto the locations of pins in a floating pin field to be used withalignment weight 100. In one embodiment, depressions 108 are disposed inrows around the perimeter of surface 106 as shown in FIGS. 1 and 2.However, it is understood that depressions 108 can be disposed at otherlocations on surface 106 so as to accommodate the layout of otherfloating pin field designs.

The size of depressions 108 may be selected to assure proper verticalalignment of the pins of the floating pin field. For example, when thepins have a diameter of approximately 0.01±0.001 inches, depressions 108may be formed with an outer diameter at surface 106 of 0.065 inches withan interior angle of 82 degrees and an inner diameter of 0.55 inches.

Alignment weight 100 further includes holes 110 that extend through athickness of alignment weight 100 in center region 107. Holes 110 allowheat to flow through alignment weight 100 toward a printed circuit boardlocated below alignment weight 100 during a reflow process. This allowselements other than pins to be soldered beneath the alignment weightwhen the pins are soldered in place.

In this embodiment, holes 110 are laid out in an array in center region107. However, it is understood that holes 110 can be located at otherpositions in alignment weight 100. Further, holes 110 are shown ascylindrical passages through alignment weight 100. Holes 110 can,however, have different sizes and shapes and are not limited to theembodiment shown.

In some embodiments, holes 110 can be omitted when only pins aresoldered during a reflow process and no other elements are placed onprinted circuit board 304 beneath alignment weight 100.

FIG. 3 is a cross-sectional view of a portion of an embodiment of anelectronic module 300 during production with alignment weight 100 inplace according to the teachings of the present invention. Alignmentweight 100 is used to assure proper contact between pins 302 and printedcircuit board 304 at solder contacts 306. Advantagously, alignmentweight 100 maintains ends 314 of pins 302 in substantially the sameplane. This reduces the likelihood that solder bridges will form at thebase of any of pins 302.

Pins 302 are held in a fixed alignment by field carrier 308. Fieldcarrier 308 is formed from flame retardant 4 (FR4) material with holesfor receiving pins 302. Field carrier 308 holds the pins in a positionthat is substantially normal to surface 307 of field carrier 308. Pins302 and field carrier 308 form floating pin field 310.

Floating pin field 310 is placed in contact with screen printed solderpaste on surface 312 of printed circuit board 304 at connection pointsfor pins 302. With floating pin field 310 in place, alignment weight 100is placed over ends 314 of pins 302 such that depressions 108 align withends 314 of pins 302. Electronic module 300 along with alignment weight100 undergo a solder reflow process to form contacts 306. Alignmentweight 100 is then removed.

As shown in FIG. 4, additional circuit components 400 are coupled toprinted circuit board 304 using, for example, surface mount technology.For example, an upgraded microprocessor can be coupled to the printedcircuit board for insertion into a computer system on printed circuitboard 304.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. For example, the alignment weight can be used with floatingpin fields for electronic modules other than a processor upgrade.Further, the location, depth, diameter, and interior angle of thedepressions 108 can be varied as necessary for a particular pin field.Further, alignment weight 100 can be formed without holes 110. Further,circuit components 400 can be coupled to both sides of printed circuitboard 304. Other materials that are resistant to warping at elevatedtemperatures and that provide sufficient weight to aid in improving thesolder bonds can be used for the alignment weight 100 in place of theUltem material described above. Other bonding materials can be used inplace of solder to connect pins 302 with printed circuit board 304.

What is claimed is:
 1. A method for coupling a floating pin field with aprinted circuit board, the method comprising: disposing a bondingmaterial on selected portions of a surface of the printed circuit board;placing a plurality of pins in a field carrier; placing the fieldcarrier and pins on the printed circuit board with the pins selectivelyaligned with the bonding material; placing an alignment weight on thepins of the pin field carrier such that the pins align with depressionsin a surface of the alignment weight; and heating the bonding materialto couple the pins with the circuit board.
 2. The method of claim 1,wherein the bonding material comprises solder.
 3. The method of claim 1,and further including aligning the alignment weight such that holespassing through a center region of the weight allow heat to pass throughthe weight to a surface of the printed circuit board.
 4. The method ofclaim 1, wherein placing the alignment weight comprises placing analignment weight that includes rows of depressions formed around theperimeter of the surface of the alignment weight.
 5. The method of claim1, wherein disposing the bonding material comprises screen printingsolder paste in selected locations on a surface of the printed circuitboard.
 6. The method of claim 1, and further comprising coupling circuitcomponents to the printed circuit board.
 7. A method for coupling afloating pin field with a printed circuit board, the comprising:disposing a solder material on selected portions of a surface of theprinted circuit board; placing a plurality of pins in a field carrier;placing the field carrier and pins on the printed circuit board with thepins selectively aligned with the solder material; placing an alignmentweight on the pins of the pin field carrier such that the pins alignwith depressions in a surface, along a perimeter of the alignmentweight; heating the solder material to couple the pins with the circuitboard; and coupling a microprocessor circuit to the printed circuitboard.
 8. The method of claim 7, and further including aligning thealignment weight such that holes formed in a center region of the weightallow heat to pass through the weight to a surface of the printedcircuit board.
 9. The method of claim 7, wherein placing the alignmentweight comprises placing an alignment weight that includes depressionsformed in a number of rows around the perimeter of the surface of thealignment weight.
 10. The method of claim 7, wherein disposing a soldermaterial comprises screen printing solder paste in selected locations ona surface of the printed circuit board.
 11. The method of claim 7, andfurther comprising coupling additional circuit components to the printedcircuit board.
 12. The method of claim 7, and further comprisingremoving the alignment weight after heating the solder material.